They must also keep swimming to keep from sinking, since most have largely or completely lost the swim bladder, the gas-filled sac that helps most other fish remain buoyant.
它们还必须不停地游动以避免下沉，因为大多数鱼基本上或完全失去了鱼鳔，这个充满气体的囊帮助大多数其他鱼保持浮力。
Indeed, the world's 37 species of seahorse are fish, breathing through gills and using a swim bladder to control their buoyancy.
事实上，世界上有37种海马是鱼，它们通过鳃呼吸，用鱼鳔来控制浮力。
Many fish larvae hatch without fully formed pectoral fins and all hatch without a swim bladder, so similar problems could occur for them.
很多小鱼孵化出来时，胸鳍还没有完全成形，而且所有的鱼孵化时都还没有形成鱼鳔。所以，它们可能会面临相似的不善于游泳的问题。
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